1. Field of the Invention
The present invention relates to a heat treatment jig used for a heat treatment boat in a vertical heat treatment furnace and a method for manufacturing the same, and more particularly to the heat treatment jig for semiconductor silicon substrates which can decrease the number of slips generated as lattice defects when heat treatment is performed to a semiconductor material such as a semiconductor silicon substrate at high temperatures, and the method for manufacturing the same.
2. Description of the Related Art
The semiconductor silicon substrate processed in an LSI device fabrication process is produced by repeating high-temperature heat treatment in steps such as oxidation, diffusion, and film deposition. In the heat treatment of the semiconductor silicon substrate, a compact installation space is realized in the vertical heat treatment furnace and the vertical heat treatment furnace is suitable for the heat treatment of plenty of large-diameter semiconductor silicon substrates. Therefore, the vertical heat treatment furnace is adopted as the apparatus to be used in various kinds of heat treatment of the semiconductor silicon substrate.
FIG. 1 shows a configuration example of the conventional semiconductor silicon substrate heat treatment boat used in the vertical heat treatment furnace. A heat treatment boat 1 includes at least three props 3, an upper end plate 5, and a lower end plate 6. The props 3 are fixed at upper and lower positions by the upper end plate 5 and the lower end plate 6. An opening 2 is provided in the heat treatment boat 1. A row of substrate support portions 4 is arranged in a multi-tier manner in the props 3. After the semiconductor silicon substrates are placed on the substrate support portions 4 from the side of the opening 2, the heat treatment boat 1 is inserted in to the vertical heat treatment furnace to perform a predetermined heat treatment.
In the case where the semiconductor silicon substrate is inserted into the vertical heat treatment furnace to perform the high-temperature heat treatment at temperatures of not less than 1100° C., when an uneven temperature distribution is generated in a surface of the semiconductor silicon substrate, a resultant thermal stress is generated in the semiconductor silicon substrate. Sometimes a stress (hereinafter simply referred to as “own-weight stress”) caused by a weight of the silicon substrate is generated depending on a method of supporting the semiconductor silicon substrate. Particularly, in the case where the heat treatment is performed to the semiconductor silicon substrate having a diameter of 300 mm using the heat treatment boat of FIG. 1, the own-weight stress has a large influence on the silicon substrate in the conventional method of supporting only an outer peripheral portion of the silicon substrate. As a result, it becomes difficult to use the heat-treated silicon substrate.
The thermal stress or the own-weight stress generates a crystal defect called a slip in the semiconductor silicon substrate during the heat treatment. Because the slip causes an increase in leak current of a LSI device or degradation of semiconductor silicon substrate flatness, conventionally various proposals are made to suppress the thermal stress or the own-weight stress.
For example, Japanese Patent Application Publication Nos. 10-242067 and 2003-100648 disclose a disc-structured heat treatment jig which supports a whole backside of the silicon substrate with a flat plate. The use of the heat treatment jig disclosed in Japanese Patent Application Publication Nos. 10-242067 and 2003-100648 can decrease a deflection displacement. However, a local temperature difference is easily generated in a region where silicon substrate to be heat-treated comes into plane contact with the heat treatment jig, and sometimes the slip is generated due to the thermal stress.
In order to solve the problem of the disc-structured heat treatment jig, there is proposed a heat treatment jig having a ring structure. Typically, Japanese Patent Application Publication No. 09-199438 discloses a heat treatment jig including a ring tray for receiving the outer peripheral portion of the silicon substrate backside. However, in the heat treatment jig including the ring tray, a central portion of the silicon substrate is bent by the own-weight, which causes the silicon substrate to come into contact with an inner peripheral end face of the ring tray. At this point, a surface flaw is generated in the silicon substrate, and the slip is generated while initiating from the surface flaw.
Japanese Patent Application Publication No. 2003-197722 discloses a ring shape (including horseshoe shape) heat treatment jig, wherein flatness and surface roughness are specified in the silicon substrate receiving surface where the silicon substrate and the heat treatment jig are in contact with each other, plural through-holes are made, being arranged in a concentric circle, in the silicon substrate receiving surface, and the total area of the through-holes is specified. In Japanese Patent Application Publication No. 2003-197722, preferably the surface roughness Ra ranges from 0.1 to 0.7 μm and the flatness is not more than 50 μm.
However, in the case of the heat treatment jig which is targeted for semiconductor silicon substrate having the diameter of 300 mm, when the flatness of not more than 50 μm is secured in the whole region where the silicon substrate is received, high-accuracy machining is required. Therefore, not only the production cost is increased, but also the realistic production conditions cannot be achieved from the viewpoint of machining accuracy.